<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style lang="css">
    button {
      z-index: 1;
      color: white;
      background: #40a9ff;
      outline: none;
      border: none;
      padding: 0.5em 1em;
    }

    button:hover {
      cursor: pointer;
      animation: jelly 0.5s;
    }

    /*  @keyframes jelly {

      0%,
      100% {
        transform: scale(1, 1);
      }

      33% {
        transform: scale(0.9, 1.1);
      }

      66% {
        transform: scale(1.1, 0.9);
      }
    } */
    @keyframes jelly {

      0%,
      100% {
        transform: scale(1, 1);
      }

      25%,
      75% {
        transform: scale(0.9, 1.1);
      }

      50% {
        transform: scale(1.1, 0.9);
      }
    }
  </style>
</head>

<body>
  <button>兔子零</button>

</body>

</html>